Cloud computing is an emerging technology that is becoming more and more popular. This is primarily due to its elastic nature: users can acquire and release resources on-demand, and pay only for those resources needed in the form of virtual machines (VMs). Elasticity allows users to acquire and release resources dynamically according to changing demands, but deciding on the right amount of resources is a difficult task since cloud applications face large and fluctuating loads. In some particular and predictable situations such as sporting or daily events, resources can be provisioned in advance through capacity planning techniques. Unfortunately, most events are widely unplanned and characterized by unpredictable load spikes of the network traffic.